Structural, microstructure and magnetic properties of superparamagnetic MnxMg1−XFe2O4 powders synthesized by sol–gel auto-combustion method

Ultrafine manganese magnesium ferrites MnxMg1−xFe2O4 powders (x = 0.2, 0.4, 0.5, 0.6, 0.8) have been synthesized using a sol–gel auto-combustion method using tartaric acid as a fuel for the first time. The effect of synthesis conditions such as annealing temperature, Mn2+ ion molar ratio and type of carboxylic acid on the crystal structure, microstructure and magnetic properties was investigated using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer, respectively. The results demonstrated that well crystalline single cubic spinel MnxMg1−xFe2O4 phase was formed at annealing temperature 1,200 °C for time 2 h. The crystallite size, lattice parameter (a) and the unit cell volume were observed to increase as the annealing temperature and the Mn2+ content were increased. The microstructure of the formed powders was synthesis conditions dependent. The produced powders were found to be well defined cubic-like structure with high homogeneity by increasing Mn2+ ion concentration up to 0.8. Furthermore, the change of carboxylic acid influenced the microstructure of the formed MnxMg1−xFe2O4 powders as the results of change of the amount of released carbon dioxide and water vapor during the annealing. The magnetic properties were sensitive to annealing temperature, Mn2+ ion molar ratio, and type of carboxylic acid. Good saturation magnetization (Ms = ~47.0 emu/g) was achieved with Mn2+ ion ratio 0.8 at annealing temperature 1,200 °C for 2 h using tartaric acid as an organic fuel whereas the maximum saturation magnetization (Ms = ~49.4 emu/g) was obtained using citric acid as a fuel at the similar conditions and Mn2+ ion content 0.5.